Since excess intake of table salt (sodium chloride) tends to cause hypertension and heart disease, or can be a factor leading to metabolic syndrome, there are increasing people worrying about intake of high-salt food materials, in particular soy sauce-containing liquid seasonings such as soy sauce and processed soy sauce. Although reduced-salt soy sauce and low-salt soy sauce have low salt content, these give an insufficient salty taste and may be added again in an additional amount, resulting in a problem of not reducing intake of table salt.
Under such circumstance, there have been proposed techniques, including that of enhancing a salty taste by replacing a part of table salt in seasoning components with potassium chloride and that of further masking an unpleasant taste of potassium to give an appropriate salty taste even low content of table salt (Patent References 1 to 9). There are also known techniques, including addition of salty taste-enhancing substances such as ornithine and glycine ethyl ester (Non-Patent References 1 and 2).
Among liquid seasonings, soy sauce (shoyu) has a wide variety of applications. It is used as is by being poured on or as a dipping sauce for sashimi (sliced raw fish), hiyayakko (cold tofu), and ohitashi (dipped cold vegetable), as well as diluted with soup stock or the like for preparing men-tsuyu (noodle soup), nabe-tsuyu (hot pot soup), and nimono (stewed food) and used for finishing sauté. The techniques using potassium chloride have problems of an insufficient salty taste and disruption of a balance in taste with increased unpleasant taste of potassium when diluted with soup stock or the like particularly for preparing nimono, and now advance not so much as to develop a practical application.
Proline is known to have effects of imparting honey-like taste to improve a taste of foods and drinks, improving a color and a fishy smell of fish sauces, and imparting a sour taste accompanied with a rich taste (Patent References 10 to 12). Proline is known to have by itself delicate sweet and bitter tastes (Non-Patent Reference 3). Isoleucine is known to have by itself an unpleasant taste and have effects of enhancing a salty taste (Non-Patent Reference 4, Patent Reference 13). Methionine is known to have effects of enhancing a rich taste, enhancing a smoky flavor, and stabilizing a flavor (Patent References 14 to 18).
There is a known liquid seasoning having an increased concentration of an amino acid produced by preparing a mixture of water and a soy sauce malt from soy beans and wheat as main ingredients, by holding it under conditions of a temperature of 40 to 60° C. and a pressure of 80 to 100 MPa without adding table salt (Patent Reference 19).